First thing I can think of is a used Tamron 17-50mm DiII (the non-VC version)... should get hold of a quality used one for less than £190. Great optics, decent AF and a fast maximum aperture make it a great zoom on crop bodies.
There's also the option of the 50mm f/1.8 (less than £100), which has a faster maximum aperture but is, of course, a fixed focal length lens so you'll have to work harder for composition and shooting position.
Think there are other fast (f/1.8 - f/2.8) primes on the market that could come under your budget but I'm not that sure of the Canon line-up (or that of 3rd party manufacturers) to give advice. Maybe look at the used market - MPB and apertureUK are good starting points...
You really want a lens (especially where zooms are concerned) that has a fixed maximum aperture and not a variable aperture as you increase the focal length on the zoom; makes for easier shooting and maximises the light.
EDIT: this is a search on WEX for Canon-fit lenses between £100-£200... gives a fair representation of what's available new. I'd ignore the long zooms and stick to wides and fast primes....
Tamron 17-50 is probably the best choice for under £200
BUT
to be honest I reckon you should look for something faster if you photograph in nightclubs. My honest opinion is that the Tamron 17-50 2.8 won't be fast enough for you (unless you are using flash). The cheaper Canon primes such as the 28. 2.8 and 50 1.8 won't be much good either since the 28 2.8 performs worse than the Tamron according to some reviews, and the 50 1.8 is too long on a crop sensor.
You should perhaps think about spending a bit more money on a Sigma 30mm 1.4 or Canon 28mm 1.8.
You might be able to get a Canon 35mm F2 for not too much more than £200 if you look really hard, although I can't remember off the top of my head how much they go for used.
I'm not sure if I'm allowed to say this but if you do go for the Tamron, I have a copy up for sale on Classified!
Tamron 17-50 is probably the best choice for under £200
BUT
to be honest I reckon you should look for something faster if you photograph in nightclubs. My honest opinion is that the Tamron 17-50 2.8 won't be fast enough for you (unless you are using flash). The cheaper Canon primes such as the 28. 2.8 and 50 1.8 won't be much good either since the 28 2.8 performs worse than the Tamron according to some reviews, and the 50 1.8 is too long on a crop sensor.
You should perhaps think about spending a bit more money on a Sigma 30mm 1.4 or Canon 28mm 1.8.
You might be able to get a Canon 35mm F2 for not too much more than £200 if you look really hard, although I can't remember off the top of my head how much they go for used.
I'm not sure if I'm allowed to say this but if you do go for the Tamron, I have a copy up for sale on Classified!